1. Field of the Invention
The present invention relates to a portable audio logic deck operated by a single driving source, and more particularly, to an apparatus for varying the tension of a belt in a portable audio logic deck.
2. Prior Art
In general, portable audio decks are divided into two groups, a manual deck having a manually-operated head, and a logic deck having an automatically-operated head. When recording on, or reproducing information from a tape cassette, the portable audio deck performs head operations, tape running and operation mode conversion with a single driving motor.
As shown in FIG. 1, a conventional portable audio logic deck includes a driving source 20 which is fixed to a main base or housing 10 and provides a rotational driving force (i.e., torque), a power transfer unit 30 which transfers the rotational force of the driving source 20, and a mode converting unit 40 which alters the mode using the transferred power. Here, the driving source 20 is formed of a single motor, and provides power to run a tape (not shown) and perform mode conversion.
The power transfer unit 30 includes a pulley 32, a pair of capstan wheels 33 and 34 rotating around a capstan axis (not shown), a main gear 35 rotating by its engagement with the capstan wheel 34, and a belt 31 which combines driving source 20, pulley 32 and the capstan wheels 33 and 34. The belt 31 is wound in an anti-rolling manner via the pulley 32 to rotate the capstan wheels 33 and 34 in opposite directions. Thus, the rotational force of the driving source 20 is transferred to the main gear 35.
The mode converting unit 40 includes a cam gear 41 having a cam groove 41a, and a main slide 43 having a hooking protrusion 43a inserted into the cam groove 41a. Cam gear 41 is selectively rotated by its interlocking engagement with main gear 35, and main slide 43 is linearly moved by the rotation of cam gear 41. The main slide 43 is kept at a stop mode position by the elastic force of a spring 45. The main slide 43 moves linearly via the rotation of the cam gear 41 to change the operating mode.
In the conventional portable audio logic deck as structured above, since the pulley 32 and the capstan wheels 33 and 34 are fixed on the main base 10, the tension of the belt 31 is not variable and a constant tension is maintained. Here, the tension of the belt 31 is set to hold the maximum load among loads generated during a forward/reverse play mode, a fast winding mode, a stop mode, and the time of mode conversion to transfer the entire power. As a result, when operating in the play mode, a smaller load is required and thus the load applied to the power transfer unit becomes greater than is needed. Such an excessive load wastes power.